Meso-Americans considered physical deformity to be the result of in-utero divine intervention and believed it to embody elements of supernatural power. For instance in the migration myth of Quetzalcoatl he was attended to by an army of dwarves and hunchbacks. Beeing attended to by hunchbacks and dwarves was apparently a pleasure and privilege of nobility, and these same Dwarves and Hunchbacks were sacrificed at the death of their masters to serve them in the afterlife. They may also have been perceived as intermediaries between the natural and the supernatural. See McCafferty & McCafferty, 2009 for more, especially p. 202

Can you go into a little more detail? I've never heard of dwarfs having any significance in Aztec Society.

To add to what /u/Gargatua13013 noted, dwarfs in Aztec society had a specific supernatural link to Tlaloc, the god of water, rain, etc. Tlaloc was served by the tlaloque, the "little Tlalocs" (in a very loose interpretation) were minor deities who were often depicted as dwarfs or children. Hence the association of Tlaloc with child sacrifice.

Tlaloc is really just the last permutation of a long line of water deities stretching back to, essentially, the start of Mesoamerican history. Chaac is the Maya analogue, but there are water/rain/storm/lake/river/etc gods in just about every major Mesoamerican civilization, They, generally, share commonalities in role, depiction, and ritual, including associations with dwarfs that stretch back to the Olmec. Karl Taube, in discussing an Olmec dwarf statuette in Pre-Columbian Art at Dumbarton Oaks (full text PDF) notes a common belief that physical deformity, like dwarfism or hunchbacks, was caused by storms and lightning, which meant those individuals represented connections the supernatural.

There's also a more mundane explanation as to why dwarfs routinely show up in Mesoamerican history, and for this I'll refer you back to Davies' The Aztecs. He makes a couple other references to dwarfs as servants, and this was not an uncommon role in which they acted. Sahagún, in Book 8 of his General History of the Things of New Spain notes that the nobles were served by "dwarfs, cripples, hunchbacks."

A very simple inference from this is that Mesoamerican nobility shared a base curiosity with dwarfs (and other non-modal body types) with elites in many of cultures. In a society, like the Aztecs, where martial prowess and social status were so very tightly connected, dwarfs, hunchbacks, and cripples were precluded from advancement. A dwarf servant in Mesoamerican thus has similarities to the way eunuchs served in Eurasian societies; they could be close, personal servants whose loyalty was (somewhat) guaranteed by their inability to assume the role of their master.